The conventional practice of transporting small boats such as outboard motor boats, is to load the boat on a trailer and tow the trailer with an automobile or truck, and when the boat is to be unloaded from the trailer, the trailer and the boat are backed into the water to the point where the boat can float away from the trailer. The trailer is then normally removed from the water. When the boat is to be removed from the water, it is loaded on the trailer by backing the trailer into the water and floating the boat onto the trailer, and after it is secured to the trailer, the trailer is towed by the vehicle from the water. Boat trailers are not only relatively heavy, bulky and expensive, but they require a substantial amount of space to store when they are not in use and are attractive objects for thieves while the boat is in the water and being used by the owner. Attempts have been made and devices have been built for attaching wheels to a boat so that the boat forms, in effect, part of a trailer capable of being towed by an automobile or truck; but these prior devices have had certain features that rendered them unsatisfactory or impractical, including difficulty of mounting the wheels on and removing them from the boat, or they are relatively complicated in construction and operation and are not easily and safely stored when the boat is being used. Further, these prior devices and parts thereof have generally been limited in use to the transporting of boats and could not be utilized or adapted for other purposes.